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I went from 20 rims to 17 rims and similar tire size and the speedometer is exactly the same. If you go up two inches in tire size you will lose 2mpg or more, you will be raising the truck which creates drag plus those tires will be more heavy. If you are going to level the truck, you can opt for 2.1 setting that will leave some rake in the truck, might help keep some mpg's that you will lose if you are totally level.
Just fyi it sounds like you aren't interested, but those are rebel knock offs 17's and you keep the OEM fit so no spacers needed. Plus they are one of the cheaper rims out there, rebel knock offs with a bunch of finish options.
Just fyi it sounds like you aren't interested, but those are rebel knock offs 17's and you keep the OEM fit so no spacers needed. Plus they are one of the cheaper rims out there, rebel knock offs with a bunch of finish options.
jws123
Senior Member
I didnt have a issue when i put 20s on mine still accurate somehow.
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same tire size or should I say width? That is what happened to me as well, as long as the tire is the same size I don't think the rim matters.
crackerjack1957
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mopar68 17" vs 20" wheel/rim size does not affect the tire height it's the tire size itself......you could put a 35" tire on both rims & they would be the same height.
tron67j
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If the rims are bigger but the tires a lower profile then the overall diameter can remain the same and thus the speed on the dash would show accurately. If the OP chooses a tire/rim package that way they are good. But, for example, if they did the following upgrade it would end up with a different overall diameter and would certainly show slower; 285/60-R17 to 35/12.5-R20 (just a number, I don't know OP current exact size). it is all about the final decision, there isn't a definitive answer until they come back with the full detail of their choice.
62Blazer
Senior Member
As mentioned, the size of the rims (the steel or aluminum part) has zero affect on the speedometer. It's all about the total height of the tires you have mounted on the rims. If you have 17" rims with tires that are 31" tall and then install 20" rims with tires that are 31" tall, it does not affect the speedometer. If you put 20" rims on the truck but the tires you use are now 33" tall than you obviously do affect the speedometer. With a taller tire the speedo will run slower, and along with that the odometer (miles) will read lower. How much different depends on how much of a difference the tire height is from stock....the taller the tire you get the more the speedo will be affected. In regards to the miles that means the truck will show you went less miles than actual, and if you hand calculate it will make the mileage look worse. You can recalibrate the speedo/odo to correct for this.
While a taller tire without recalibrating the speedo/odo will make the mileage appear worse, generally when you put a taller/bigger tire on a truck you decrease the actual MPG. There are several variables, but a bigger tire is usually heavier and increased size means it has more leverage. Overall that means it is harder to turn and the engine has to put out more power to do so. Another big factor is the rolling resistance, and a more aggressive tire usually has more rolling resistance. So if you go from a 31" highway tread tire to a 33" mud tire I would expect it to make a pretty big difference.
In the end, if you put on taller tires without calibrating the speedo/odo the fuel mileage will be worse both by the fact the miles aren't correct and the tires themselves are decreasing the mileage.
While a taller tire without recalibrating the speedo/odo will make the mileage appear worse, generally when you put a taller/bigger tire on a truck you decrease the actual MPG. There are several variables, but a bigger tire is usually heavier and increased size means it has more leverage. Overall that means it is harder to turn and the engine has to put out more power to do so. Another big factor is the rolling resistance, and a more aggressive tire usually has more rolling resistance. So if you go from a 31" highway tread tire to a 33" mud tire I would expect it to make a pretty big difference.
In the end, if you put on taller tires without calibrating the speedo/odo the fuel mileage will be worse both by the fact the miles aren't correct and the tires themselves are decreasing the mileage.
Jeepwalker
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There's a few other scanners which can change the wheel/tire size, if you have a buddy with a good one. A Snap-on scanner can for sure. An el-cheapo one won't though. AlfaOBD is usually the least expensive route. The software and tire sizes menu resides in the truck computer...yer just selecting from a list of available sizes and choosing a different one to match the new wheel/tire.
